The present invention relates to a facsimile system and, in particular, to a re-dial control method of performing a nonstandard capability message transmission between facsimile systems.
Generally, in the case of a terminal equipment which transmits and receives a message by means of a data transmission network like a facsimile, various control information is exchanged between the elements included in a data transmission network. The control information aforementioned is called a protocol that includes control information exchanged between the terminal equipments. Relay-Request, Call Selection, Call Release, Message Transmitting and Receiving Flow Control may be a good example of the protocol.
Such rules of protocol are given in the CCITT (Comite Consultatif International Telegraphique et Telephonique) recommendation T.30.
In order to transmit a message between facsimile systems by means of the public switched telephone network (PSTN) now in use, the protocol applied in the CCITT recommendation T.30 must be satisfied. That is to say, if an exchange of the protocol is not made at an appropriate time, transmission of a message between facsimile systems may not be achieved.
"Non-standard capability" in a facsimile system which exchanges a protocol with its counterpart station in the aforesaid manner means various capability services including a Relay-Request, a Mail Box and a Transmission-Receiving (Tx-Rx) Journal Report. Such non-standard capability services as described hereinabove are usually controlled by a center (called) facsimile system. When such non-standard capability services are requested by an originator (calling) facsimile system, such services are provided by the center facsimile system. Such non-standard capability services between the originator facsimile system and center facsimile system are also performed by exchanging the protocol commands and the request for the non-standard capability services is based upon the signaling format given in the CCITT recommendation T.30.
Referring to the conventional non-standard capability services between facsimile systems, when the center facsimile system which can provide various non-standard capability services is dialed by the originator facsimile system, an on-line connection is formed between these facsimile systems. When a request is made by the originator facsimile system to the center facsimile, the center facsimile system determines if such a specific non-standard capability service as requested can be provided. In case it is possible, the center facsimile system provides the non-standard capability service to the originator facsimile.
However, the prior art facsimile system has some problem with re-dialing when the non-standard capability services are performed. That is, when a request for a specific non-standard capability service is made by the originator facsimile system to the center facsimile system, an error is committed because the called facsimile is in a condition where it does not transmit to the calling facsimile system the inexecutability of such a specific non-standard capability service as requested when it is not in a condition to provide the non-standard capability service.
On the other hand, the originator facsimile system which made a request for a specific non-standard capability service has always performed re-dialing to the extent of a previously set number, as the originator facsimile system is not provided with the requested specific non-standard capability service. Such re-dial operation is performed in the same way even if an error is committed when a non-standard capability service is performed.
Therefore, the originator facsimile system performs the redial operation continuously, nevertheless the originator facsimile system is not provided with the specific non-standard capability service. Consequently, the originator facsimile system has occupied a communication line only to be imposed an unnecessary telephone charge.